This disclosure relates to double row thrust bearings; and, more particularly, to double row tapered roller thrust bearings having an increased load capacity without a concomitant increase in the size of the bearing.
The increasing demand for power density in mechanical systems often requires a rolling element bearing to support increased loads while occupying the same, and in some instances, a smaller space. For example, in the oil and gas industry, the thrust load on a top drive assembly has increased 20%; while, at the same time, the envelope size for the supporting bearing has remained the same. Doing so has made it possible to avoid redesign of the drive system. Because of this and similar situations, bearing makers are now challenged to meet this new demand of developing new bearings having an improved load carrying capacity while still fitting within the same space as previous bearings having less load carrying capacity.
Thrust roller bearings have higher axial load carrying capacities than their ball bearing counterparts. Further, tapered roller thrust bearings are often favored over cylindrical thrust bearings because of the essentially pure rolling motions between a roller body (i.e., rolling element) and its raceway contacts. This pure rolling motion results from the so-called “on apex” design as illustrated in FIG. 1. In an on-apex design, the diameter of a rolling element (roller) R tapers down towards the apex A of a single row thrust bearing assembly BA. This results in a reduced effective contact radius as the area of contact between roller R and its raceway W moves closer to the bearing's axis X. This, in turn, has a negative impact on the bearing's load carrying capacity. The present disclosure is directed to a novel design which overcomes this deficiency of single row thrust tapered roller bearings. Previous attempts at increasing the load bearing capacity of a double row thrust bearing assembly have been made. See, for example, Japanese patent publication 2007270968A which employs both needle rollers and tapered rollers.